1. Field of the Invention
The present invention relates to a clamping mechanism that secures a workpiece to a mechanical arm. More particularly, the present invention relates to a clamp that gently secures a semiconductor wafer to a robot blade by biasing the wafer against a retaining member at the forward edge of the blade when the robot blade is at least partially retracted for rotation.
2. Background of the Related Art
Modem semiconductor processing systems include cluster tools which integrate a number of process chambers together in order to perform several sequential processing steps without removing the substrate from a highly controlled processing environment. These chambers may include, for example, degas chambers, substrate preconditioning chambers, cooldown chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers, etch chambers, and the like. The combination of chambers in a cluster tool, as well as the operating conditions and parameters under which these chambers are run, are selected to fabricate specific structures using a specific process recipe and process flow.
Once the cluster tool has been set up with a desired set of chambers and auxiliary equipment for performing certain process steps, the cluster tool will typically process a large number of substrates by continuously passing substrates through a series of chambers and process steps. The process recipes and sequences will typically be programmed into a microprocessor controller that will direct, control, and monitor the processing of each substrate through the cluster tool. Once an entire cassette of wafers has been successfully processed through the cluster tool, the cassette may be passed to yet another cluster tool or stand alone tool, such as a chemical mechanical polisher, for further processing.
Typical cluster tools process substrates by passing the substrates through a series of process chambers. In these systems, a robot is used to pass the wafers through a series of processing chambers. Each of the processing chambers is constructed to accommodate and process two wafers at a time. In this way, throughput of substrates in the cluster tool is effectively doubled. The amount of time required by each process and handling step has a direct impact on the throughput of substrates per unit of time. While the exact design of an integrated circuit fabrication system may be complex, it is almost always beneficial to perform each step as quickly as possible to maximize overall throughput without detrimentally affecting product quality, operating costs, or the life of the equipment.
Substrate throughput in a cluster tool can be improved by increasing the speed of the wafer handling robot positioned in the transfer chamber. As shown in FIG. 1, the magnetically coupled robot comprises a frog-leg type connection or arms between the magnetic clamps and the wafer blades to provide both radial and rotational movement of the robot blades in a fixed plane. Radial and rotational movements can be coordinated or combined in order to pick up, transfer, and deliver substrates from one location within the cluster tool to another, such as from one chamber to an adjacent chamber.
Another exemplary robot is shown in FIG. 2. FIG. 2 shows a conventional polar robot with an embodiment of the substrate clamping apparatus of the present invention. As shown in FIG. 2, like the xe2x80x9cfrog-legxe2x80x9d type robot of FIG. 1, radial and rotational movements may be coordinated or combined in order to pick up, transfer, and deliver substrates from one location within a cluster tool to another, such as from one chamber to an adjacent chamber. However, unlike the robot in FIG. 1, the robot shown in FIG. 2 may also provide translational movement of wafer 302.
As the robot speed and acceleration increase, the amount of time spent handling each substrate and delivering each substrate to its next destination is decreased. However, the desire for speed must be balanced against the possibility of damaging the substrate or the films formed thereon. If a robot moves a substrate too abruptly, or rotates the wafer blade too fast, then the wafer may slide off the blade, potentially damaging both the wafer and the chamber or robot. Further, sliding movements of the substrate on the wafer blade may create particle contaminants which, if received on a substrate, can contaminate one or more die and, thereby, reduce the die yield from a substrate. In addition, movement of the substrate on the wafer blade may cause substantial misalignment of the substrate that may result in inaccurate processing or even additional particle generation when the substrate is later aligned on the support member in the chamber.
The robot blade is typically made with a wafer bridge on the distal end of the wafer blade that extends upwardly to restrain the wafer from slipping over the end. However, the wafer bridge does not extend around the sides of the blade and does very little to prevent the wafer from slipping laterally on the blade. Furthermore, the wafers are not always perfectly positioned against the bridge. Sudden movement or high rotational speeds may throw the wafer against the bridge and cause damage to the wafer or cause the wafer to slip over the bridge and/or off the blade.
There is a certain amount of friction that exists between the bottom surface of a wafer and the top surface of the wafer blade that resists slippage of the wafer. However, the bottom surface of a silicon wafer is very smooth and has a low coefficient of friction with the wafer blade, which is typically made of nickel plated aluminum, stainless steel or ceramic. Furthermore, a typical wafer is so lightweight that the total resistance due to friction is easily exceeded by the centrifugal forces applied during rapid rotation of the robot, even when the blade is in the fully retracted position. However, this low coefficient of friction is typically relied upon when determining the speed at which a robot rotates.
Patent application Ser. No. 08/935,293, entitled xe2x80x9cSubstrate Clamping Apparatus,xe2x80x9d filed on Sep. 22, 1997, which is hereby incorporated by reference discusses the problem of wafer slippage on a robot blade and the need to increase wafer transfer speeds. This application describes a clamping mechanism that holds the substrate on the blade during transfer. However, that invention is directed to a complex lever/flexure system to engage and disengage the clamp fingers.
There is a need for a robot that can transfer wafers at increased speeds and acceleration/decelerations, particularly in a multiple or single substrate processing system. More specifically, there is a need for a wafer clamping mechanism on a robot that can secure a wafer or a pair of wafers on a wafer blade or a pair of wafer blades with sufficient force to prevent wafer slippage and wafer damage during rapid rotation and radial movement.
In one aspect, the present invention is directed to a clamp wrist for a robot assembly having one or more arms and one or more actuators for driving the arms to handle a workpiece, comprising a wrist housing pivotally coupled to the arms; at least one clamp finger disposed in the wrist housing; and a biasing member coupled to the at least one clamp finger for urging the at least one clamp finger against the workpiece. A particular feature of this aspect of the invention is that a translational member may be coupled to at least one of the arms; and a contact pad may be movably connected to the clamp finger. Further, the clamp finger may be pivotally mounted to the wrist housing; and the contact pad may be positioned to move the clamp finger away from the workpiece when the robot arm reaches a given degree of extension. Further, a stop member may be attached to the wrist housing and adapted and positioned to limit the movement of the clamp finger away from the workpiece. Still further, the biasing member may be one spring, and two clamp fingers may be mounted in spaced relation to one another and the spring may be attached to the clamp fingers.
In another aspect, a translational member may be coupled to at least one of the arms; a flexure member may be movably connected to at least one clamp finger; and a contact pad may be coupled to the flexure member and adapted and positioned to engage at least one clamp finger and move at least one clamp finger away from the workpiece when the robot arm reaches a given degree of extension. Further, two clamp fingers may be mounted in spaced relation to one another; and the flexure member may be attached to the clamp fingers and adapted to cause the clamp fingers to move apart and away from the workpiece upon engagement of the translational member with the contact pad. Still further, a lever may be pivotally mounted to the wrist housing and adapted and positioned to engage the contact pad of the flexure member upon engagement of the lever by the translational member.
In another aspect, the present invention is directed to a clamping mechanism for securing a workpiece to a workpiece handling member coupled to the distal end of a robot arm, the workpiece handling member comprising a wafer handling blade having a workpiece receiving region and a retaining member at the distal end thereof, comprising at least one clamp finger adapted and positioned to contact the edge of the workpiece and a biasing member coupled to at least one clamp finger adapted to urge the clamp finger against the workpiece when the workpiece is positioned on the workpiece receiving region to clamp the workpiece between the clamp finger and the retaining member. A feature of this aspect of the invention is that the clamping mechanism may comprise a lever arrangement coupled to the clamp finger adapted to move the clamp finger away from the workpiece when the workpiece handling member and the robot arm are extended. Another feature of this aspect of the invention is that the lever arrangement may be adapted to be engaged by the relative angular rotation between the robot arm and the workpiece handling member; the clamp finger may be pivotally mounted to the workpiece handling member; and a translational member may be attached to the robot arm positioned and adapted to engage the clamp finger and move the clamp finger away from the workpiece when the robot arm reaches a given degree of extension. Yet another feature of this aspect of the present invention is that the lever arrangement may further comprise: a flexure member movably connected to the clamp finger; and a contact pad coupled to the flexure member for selective engagement with the translational member, and adapted and positioned to engage the clamp finger and move the least one clamp finger away from the workpiece when the robot arm reaches a given degree of extension. Still another feature of this aspect of the present invention is that the lever arrangement may further comprise a lever pivotally mounted to the workpiece handling member. The lever may have an end portion; a contact pad may be coupled to the lever proximate the end portion for selective mating with the translational member; and the contact pad of the flexure member may be positioned for selective mating with the lever, whereby engagement of the lever by the translational member causes engagement of at least one clamp finger to move the clamp finger away from the workpiece when the robot arm reaches a given degree of extension. Further, two clamp fingers may be mounted in spaced relation to one another; and the flexure member may be attached to the clamp fingers and adapted to cause the clamp fingers to move apart upon engagement of the translational member with the contact pad. Still further, a stop member may be attached to the workpiece handling member and adapted and positioned to limit the movement of the at least one clamp finger away from the workpiece.
In yet another aspect, the present invention may be directed to a robot arm assembly, comprising: a pair of frog-leg type robot arms, each arm having a distal end with a clamp wrist attached thereto; the clamp wrist comprising a wrist housing pivotally coupled to the robot arm; at least one clamp finger disposed in the wrist housing; and a biasing member coupled to the at least one clamp finger adapted to urge the at least one clamp finger against a workpiece. A feature of this aspect of the invention is that a translational member may be attached to the distal end of the robot arm; and a lever arrangement may be connected to the at least one clamp finger and adapted and positioned for engagement by the translational member to cause the at least one clamping finger to move away from the workpiece when the robot arm reaches a given degree of extension. Another feature of this aspect of the present invention is that a stop member may be attached to the wrist housing and adapted and positioned to limit the movement of the at least one clamp finger away from the workpiece.
In still another aspect, the present invention may be directed to a robot, comprising a pair of first hub members rotatable about a first axis; a pair of magnetic drives for driving each of the hub members; a pair of robot arms, each robot arm comprising a first and second strut, the first strut mounted to a hub member; a translational member disposed on each of the second struts; a workpiece handling member pivotally attached to the pair of robot arms, the workpiece handling member comprising at least one clamp finger; a biasing member coupled to the at least one clamp finger adapted to urge the at least one clamp finger against a workpiece; a lever arrangement adapted and positioned to engage the at least one clamp finger in response to engagement by the translational member when the attached arm assembly reaches a given degree of extension; and the lever arrangement adapted to pull the at least one clamp finger away from the workpiece when the attached arm assembly reaches a given degree of extension. A feature of this aspect of the invention is that the biasing member is at least one spring. Another feature of this aspect of the invention is that a lever may be pivotally mounted to the wrist housing and a stop member may be attached to the wrist housing and adapted and positioned to limit the movement of the at least one clamp finger away from the workpiece. Another feature of this aspect of the present invention is that rotations of the first and second arms in a same direction may be converted into one of the two independent motions and rotations of the first and second arms in opposite directions may be converted into another of the two independent motions.
In yet another aspect, the present invention may be directed to a robot arm assembly, comprising a pair of frog-leg type robot arms, each arm having a distal end with a clamp wrist attached thereto; the clamp wrist comprising a wrist housing pivotally coupled to the robot arm; a plurality of opposing clamp fingers operatively connected to the wrist housing; and a biasing member coupled to the clamp fingers adapted to urge the clamp fingers against a workpiece. A feature of this aspect of the invention is that the opposing clamp fingers may include a first, proximal clamp finger or set of clamp fingers and a second distal clamp finger or set of clamp fingers. Another feature of this aspect of the invention is that a common linkage may be attached or otherwise operatively connected to the opposing clamp fingers to engage and/or disengage the clamp fingers. Another feature of this aspect of the invention is that the common linkage may be a length of wire, a segment of spring steel, or other suitable members.